Well, I have sailed my 16 with over 400lbs before. I went out with two other friends and our total weight was probably around 450lb. I can tell you though, the boat will handle much differently as compared to when you will singlehand it. Of course, it will be more sluggish with 400+lbs and less wind, but having two other friends on board in a heavy wind is always fun because you can have more weight on the rails and you can really get moving with that much weight on the trapeze to counter the force of the wind. I would say experiment with it though, you know your boat better than anyone else, and if its an older boat and you feel uncomfortable, then don't do it. If its an older boat, you may also notice that it will sink down quite a bit and this could mean that more water is in your hulls. I have an older boat, and I always end up draining my hulls after I sail with more than two people on it.